Each cell (blastomere) of th 8-cell mouse embryo becomes functionally and morphologically polarized around the time of compaction. Early 8-cell blastomeres are covered with a uniform distribution of microvilli (MV), bind a variety of fluorescent ligands uniformly over their surfaces, have a randomly located nucleus and display a random cytoplasmic distribution of endocytotic vesicles. Late 8-cell blastomeres are polarized with stable MV restricted to the free surface of each cell, fluorescent ligand-binding most intense at the MV pole, a basally-placed nucleus and endocytotic vesicles arranged in a column extending from the nucleus to the MV pole. This 8-cell polarization is crucial to further embryonic development because it forms the basis for the foundation of the two cell lineages leading to the inner cell mass and trophectoderm of the blastocyst. Little is known about the mechanisms which underlie the processes of induction, polarization and maintenance of polarity in these cells. Therefore, in this project, we will attempt to elucidate the mechanisms underlying these processes. The metabolic requirements (energy, RNA, DNA, protein synthesis, etc.) and possible mechanisms for these processes will be probed with a variety of pharmacological agents. In addition, our knowledge of the specificity of the induction process will be extended by testing cells of embryonic, adult or tumor origin, cross-linked (fixed) embryonic cells and various matrices as possible inducers. It is hoped that these studies will not only shed light on polarization in early mouse embryos but may provide insight into the general problem of differentiation and polarization of other epithelial-like cells.